This invention is directed to a telephone fault detection system for in-line installation with telephone company trunk lines and, in particular, to a fault detection system that provides an indication of the occurrence of a fault condition in a telephone system and whether the fault condition is with the telephone company or in a customer's telephone equipment.
Heretofore, fault isolation systems for determining whether a fault condition occurs in a professional telephone system have been provided in order to deal with problems that are normally associated with the installation of professional communication equipment, such as private branch exchanges (PBX's) and key systems (KSU's). Such equipment is either leased from a local telephone company or purchased from a private company and, in either instance, is connected to a local telephone company's dial central office over leased telephone trunks.
When a fault condition occurs within a telephone system that includes a leased telephone trunk and customer owned professional equipment, the fault condition is not necessarily in the telephone company trunk line. Although the telephone company will test and repair its own leased equipment, it will not accept the responsibility for customer owned equipment. When the telephone company is required to make a service call and ultimately determines that the trouble lies within the customer owned equipment, the customer is then charged for a customer call thereby providing a considerable disincentive to the ownership of customer owned equipment. This disincentive has further discouraged the purchase of non-professional type private telephone equipment for use in homes, apartments and small businesses.
A system for facilitating a determination whether a fault condition lies with the customer owned commercial equipment or with the telephone company equipment is disclosed in U.S. patent application Ser. No. 169,715, filed on July 17, 1980 now abandoned. The system disclosed in application No. 169,715, however, is limited to the use of an extrinsic monitoring device that has no utility in the customer owned telephone system other than to detect a fault condition and, for this reason, is neither practical nor satisfactory for a non-professional private telephone system of the type to be found in a home, apartment or small business facility. Furthermore, the fault isolation device described in applicants' U.S. patent application Ser. No. 169,715 does not provide a visual fault indication. Accordingly, a telephone fault detection system for in-line installation between a telephone company trunk line and a privately owned or leased telephone system that is capable of providing a visual indication of a fault condition when the system is in a normal operating mode and is further capable of discerning if the problem is located in the internal telephone equipment or with the telephone company is desired.